The invention is in the field of physics of computation. More particularly, the invention relates to the ability to use microscopic particles, especially in a mechanical way, to perform calculations.
The silicon transistor technology on which modem computation is based has shown rapid exponential improvement in speed and integration for more than four decades. It is widely expected that this rate of improvement will slow as device dimensions approach the nanometer scale (see J. D. Meindl et al., xe2x80x9cLimits on silicon nanoelectronics for terascale integrationxe2x80x9d, Science 293, pp. 2044-2049, 2001). This has led to the exploration of many alternative computation schemes, most of which are based on gating the flow of electrons by novel means such as quantum dots (see D. Goldhaber-Gordon et al., xe2x80x9cOverview of nanoelectronic devicesxe2x80x9d, Proc. IEEE 85, pp. 521-540, 1997), organic molecules (see G. Y. Tseng et al., xe2x80x9cToward nanocomputersxe2x80x9d, Science 294, pp. 1293-1294, 2001), carbon nanotubes (see S. J. Wind et al., xe2x80x9cVertical scaling of carbon nanotube field-effect transistors using top gate electrodesxe2x80x9d, Appl. Phys. Lett. 80, pp. 3817-3819, 2002), and the motion of single atoms or molecules (see Y. Huang et al., xe2x80x9cLogic gates and computation from assembled nanowire building blocksxe2x80x9d, Science 294, pp. 1313-1317, 2001). Other proposals include electrons confined in quantum dot cellular automata (see C. S. Lent et al., xe2x80x9cA device architecture for computing with quantum dotsxe2x80x9d, Proc. IEEE 85, pp. 541-557, 1997; and I. Amlani et al., xe2x80x9cDigital logic gate using quantum-dot cellular automataxe2x80x9d, Science 284, pp. 289-291, 1999), magnetic dot cellular automata (see R. P. Cowburn et al., xe2x80x9cRoom temperature magnetic quantum cellular automataxe2x80x9d, Science 287, pp. 1466-1468, 2000), and solutions of interacting DNA molecules (see R. S. Braich et al., xe2x80x9cSolution of a 20-variable 3-SAT problem on a DNA computerxe2x80x9d, Science 296, pp. 499-502, 2002).
Computation can also be achieved using purely mechanical means (see D. D. Swade et al., xe2x80x9cRedeeming Charles Babbage""s mechanical computerxe2x80x9d, Scientific American, pp. 8691, Feb. 1993; and K. E. Drexler et al., Nanosystems, John Wiley and Sons, New York, 1992). It has been widely assumed that mechanical devices will always be too large to be competitive with electronic computational devices. Atomic scale mechanical devices capable of performing logic computations would, however, be of interest to the computational technology community.
Preferred embodiments and implementations of the invention involve a type of mechanical computation in which the moving parts are single molecules bound to a surface. A molecule moves or xe2x80x9chopsxe2x80x9d on the surface from a site of higher potential energy to an adjacent site of lower potential energy, with this movement being controlled by chemical interactions with nearby molecules. This movement may be viewed as being analogous in some respects to the toppling of rows and/or columns of standing dominoes, in which the motion of a molecule to a lower-energy position corresponds to the toppling of a domino.
Moving a single molecule in a row of molecules causes others to move or xe2x80x9ctopplexe2x80x9d sequentially, so that a single bit of information can be transported from one location to another, with the toppled and untoppled states representing binary 0 and 1, for example. In addition, the molecules described herein may be arranged in patterns that perform logic operations. For example, an OR gate is implemented by a molecule that is toppled as a result of an interaction with either one of two arriving molecule cascades. An AND gate, on the other hand, is implemented by a molecule that is toppled as a result of an interaction with two arriving molecule cascades. One side-effect of moving a molecule from a position of higher potential energy to one of lower potential energy is that energy is dissipated in the process, thereby producing heat to be removed later. Thus, it is advantageous to use the least difference in potential energy sufficient to give the desired speed of the cascade, provided the activation energy (the potential energy barrier against motion from the initial position) is not so small that the initial configuration has an unacceptable probability of undergoing spontaneous decay, i.e., motion to the lower energy position.
One preferred embodiment of the invention is an array of discrete, microscopic particles that are initially in a substantially fixed spatial relationship with respect to each other and with respect to a matrix that acts as a host material for holding the particles. Each of the particles in the array includes at least one atom (either neutral or charged), and the array includes at least first, second, and third ones of the particles. The particles are arranged to perform a logic computation, so that in response to at least one of the first and the second particles being urged into a lower potential energy state, movement of the third particle is induced as a result of at least one of i) physical interaction between the first particle and the third particle and ii) physical interaction between the second particle and the third particle. The array may form an AND gate, in which case movement of the third particle is induced as a result of i) physical interaction between the first particle and the third particle and ii) physical interaction between the second particle and the third particle. Alternatively, the array may form an OR gate. The array may be tailored to longer cascade lengths by including additional particles; fourth and fifth particles may be included in the array, such that movement of the first particle is induced as a result of moving a fourth particle in the array (in which the fourth particle physically interacts with the first particle), and such that movement of the second particle is induced as a result of moving a fifth particle in the array (in which the fifth particle physically interacts with the second particle). In a preferred embodiment, the particles are molecules arranged on a surface of the matrix. Additional particles may be included in the array to increase the rate at which the cascade of motion propagates through the array, e.g., the presence of such additional particles acts to induce movement of the third particle more quickly than would occur in the absence of the additional particles.
One preferred implementation of the invention is a method of propagating motion through an array of microscopic particles that are initially in a substantially fixed spatial relationship with respect to each other and with respect to a matrix that acts as a host material for holding the particles, in which each of the particles includes at least one atom. The method includes selecting a first one of the particles, and moving the first particle, so that (i) movement of a second particle that is in proximity with the first particle is induced as a result of physical interaction between the first particle and the second particle, and (ii) movement of a third particle that is in proximity with the second particle is induced as a result of physical interaction between the second particle and the third particle. The method further includes sequentially inducing movement of other particles in the array in a similar fashion, so that motion propagates through the array, in which the propagation of motion represents information. In a preferred implementation, the movement includes translational movement of particles across a surface of the matrix, and the second particle is adjacent to the first particle. In preferred implementations of the method, not all of the particles move as the cascade of motion propagates through the array.
Another preferred implementation of the invention is a method of propagating motion through an array of microscopic particles that are initially in a substantially fixed spatial relationship with respect to each other and with respect to a matrix that acts as a host material for holding the particles, in which each of the particles includes at least one atom. The method includes selecting a first one of the particles, and moving the first particle, so that (i) movement of a second particle that is in proximity with the first particle is induced as a result of physical interaction between the first particle and the second particle, and (ii) movement of a third particle that is in proximity with the second particle is induced as a result of physical interaction between the second particle and the third particle. The method further includes sequentially inducing movement of other particles in the array in a similar fashion, without inducing movement of all the particles in the array, so that motion propagates through the array, in such a way that the chemical structure of the particles remains unaltered during the propagation. In a preferred implementation, the movement includes translational movement of particles across a surface of the matrix, and the second particle is adjacent to the first particle. In preferred implementations of the method, the propagation of motion represents information.
Yet another preferred implementation of the invention is a method of performing logic computations that includes providing an array of discrete microscopic particles, each of which includes at least one atom, with the array including at least first, second, and third ones of the particles. The method includes moving at least one of the first and second particles, and inducing movement in the third particle as a result of at least one of i) physical interaction between the first particle and the third particle and ii) physical interaction between the second particle and the third particle, in which the third particle is urged into a lower potential energy state, and in which movement of the third particle represents output of a logic computation. The array of discrete particles may form an AND gate, in which case the method includes moving the first particle (thereby urging the first particle into a lower potential energy state), and moving the second particle (thereby urging the second particle into a lower potential energy state), in which movement of the third particle is induced as a result of i) physical interaction between the first particle and the third particle and ii) physical interaction between the second particle and the third particle. Alternatively, the array of discrete particles may form an OR gate. In a preferred implementation of the method, the particles hop from one site on a surface of the matrix to an adjacent site on the surface.